GLB export has correct wireframe, but wrong render. What am I missing?
Per comments above, the solution was to recalculate the normals, and upgrade to the version of Blender.
In the screenshots, it looks like some polygons face the camera, while others face away.  If &quot;Backface culling&quot; is turned on (as a material property setting in Eevee), glTF will treat these polygons as single-sided, and may not render the ones facing the other way.  The fix could be as easy as Mesh -&gt; Normals -&gt; Recalculate Outside, to get them all to face the same way.  But if they need to be visible from both sides, make sure &quot;Backface culling&quot; is turned off under Eevee's material settings (not to be confused with a viewport option by the same name, that will have no effect on glTF export).
Also, Blender 2.90 includes several fixes to the glTF exporter, some related to normal vectors, so upgrading is recommended.